1. Field of the Invention
The present invention relates to a recording method and recording apparatus for recording information, such as images and characters, particularly information, such as color images and characters using color tones of K, C, M and Y colors, on a recording medium.
2. Description of the Related Art
For the recording of images and characters, there is known a recording method in which an image receiving sheet and a transfer sheet are layered one on the other, and in this state, are fixed onto a drum, and those are exposed to laser light. In this case, the image receiving sheet is wound around the drum in a state that its image receiving layer is directed upward. The transfer sheet is wound on the drum in a state that its toner layer is layered on the image receiving layer of the image receiving sheet. A recording head of the laser exposure type is reciprocatively moved in directions parallel to the rotational shaft of the drum. The recording head emits laser light and takes the form of a plurality of spots of light when it lands on the recording medium. The plural spots 1, as shown in FIG. 15, are linearly arrayed in the moving direction of the recording head. In the recording method, the rotational direction of the drum is coincident with a main scan direction, and the moving direction of the recording head is coincident with a sub scan direction. Accordingly, when the rotational motion of the drum and the linear motion of the recording head are combined, the transfer sheet is scanned with the spots to thereby transfer a desired image on the image receiving sheet.
In the recording method, optical energy of the laser light is transduced into thermal energy by the optical-to-thermal transducing layer at a recording local area or part irradiated with the laser spots. At this time, the heat generation is instantaneously performed, and water and organic solvent, which are contained in the optical-to-thermal transducing layer and the toner layer, are volatilized, and called gas is generated. Accordingly, in the recording method in which the image receiving sheet and the transfer sheet are layered one on the other, and an acting layer acting in connection with the laser light is sandwiched between those sheets, the gas generated is hard to run out into the air, and stays between the image receiving sheet and the transfer sheet.
At both ends of the spot array, the gas is easy to run out in the sub-scan direction (the right side or left side in FIG. 15). At the central part of the spot array, the generated gas is hard to run out in the sub-scan direction, and it stagnates at the central part of the spot array.
At the central part of the spot array, the generated gas is put between the toner layer and the image receiving layer, so that the toner layer and the image receiving layer are not in close contact with each other. In this state, the toner layer is not transferred to the image receiving layer even at a part of the recording medium irradiated with the laser light. As a result, no color or thin color is formed on that part in the final image. When this phenomenon is observed macroscopically (by the eye), a stripe (vertical stripe) 3 appears which extends in the drum rotational direction, as shown in FIG. 15, and it will be an image defect.
For example, when 32 spots are arrayed at an interval of 10 μm (2450 dpi), a distance between the spots located at both ends of the spot array in the sub-scan direction, is 310 μm. In an another example where 256 spots are arrayed at an interval of 10 μm (2450 dpi), a distance between the spots located at both ends of the spot array in the sub-scan direction, is 2550 μm. As the spot-to-spot distance between both ends of the spot array becomes larger, the gas is harder to run out at the central part, and also when it is observed by the eye, it becomes the image unevenness and it is easily recognizable.
To be more specific, the gas stagnates at the central part of the spot array, and the toner layer and the image receiving layer are not in close contact with each other. In this state, heat generated in the optical-to-thermal transducing layer of the transfer sheet does not flow to the image receiving layer; in a usual case, it flows to the latter. And heat is accumulated in the transfer sheet. The result is that the optical-to-thermal transducing layer of the transfer sheet and the toner layer are heated and its temperature is higher than that in the normal state. When the temperature rises till the optical-to-thermal transducing layer and the toner layer are decomposed, gas is further generated, and the optical-to-thermal transducing layer and the toner layer are molten and decomposed to thereby lose their normal state. In this state, an optical density at the central part is low, or the optical-to-thermal transducing layer, which should not be transferred, is transferred onto the image receiving layer. More serious image defect occurs.